As described in my aforementioned patent, a hydraulic percussion apparatus comprises a body providing an inlet for the hydraulic pressure medium and an outlet therefor. The outlet forming part of a low-pressure hydraulic circuit while the inlet forms part of a high-pressure hydraulic circuit.
Within this body, there is reciprocatable a stepped piston which constitutes the striking or impact mass and is alternately driven toward and retracted from the end of a tool which is received in this body.
When the piston is driven toward the end of the tool, it strikes the latter, delivering an impact which can be used for a variety of purposes.
For example, the tool may be a chisel or other rock-breaking implement which can be used to break up pavement, concrets or mineral matter. The tool may also be a drill bit which is driven by the apparatus, a tamper or rammer adapted to compact a body of material, or an element forming a hammer to drive piling, posts or the like.
The apparatus may be manipulated by hand or mounted on a vehicle.
In principle, the high-pressure hydraulic circuit delivers the hydraulic medium under pressure to the large diameter end of the impact mass or piston to drive it against the tool and to a shoulder between the large diameter and small diameter portions of the piston to lift the piston away from the tool.
In order to control the reciprocation of the piston, there is provided within the cylinder above the piston, a distributor which is slidably mounted in the cylinder and alternately connects the chamber above the piston with the high pressure hydraulic medium circuit and with the low pressure hydraulic circuit or outlet to cause the reciprocation of the piston.
In the aforementioned patent this distributor is slidable above the piston and is caused to move rectilinearly alternately up and down, with a cadence which determines the impact frequency of the apparatus.
An essential part of this distributor, which has the configuration of a relatively massive sleeve, is an outwardly extending shoulder or collar which has a larger diameter than the remainder of the body of the distributor and than the diameter of the larger part of the striking mass or piston.
This collar or shoulder, at a given instant in the cycle, by the differential-piston effect, initiates the descent of the distributor.
While this construction has been found to represent a major advantage in impact-generating tools over the prior art described in the patent, it has been found to have a disadvantage. The speed of descent of the distributor is limited by hydrodynamic braking caused by the fact that the chamber connected to the low pressure side of the circuit is evacuated in a very brief time.
The shoulder, which has heretofore been considered indispensable to the functioning of the device, limits the speed of descent and produces a delayed opening of the flow passages so that the opening is not clean and the operation of the system is adversely affected.
In addition, the displacement of the distributor is necessarily limited by the presence of the shoulder which requires precise machining of two coaxial parts on the distributor having different diameters. This increases the cost of the apparatus and creates technological difficulties.